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Problem with separating parts for multicolor 3d print

Message 1 of 10
2488 Views, 9 Replies

Problem with separating parts for multicolor 3d print


I'm having a problem with meshmixer. I'm a chemist and trying to print a multicolor crystal structure (I have a 3d printer with a multi color upgrade). To do that I produce an .stl of the crystal structure.

.stl after importing.stl after importing

Then I make it into a solid so it's ready for 3d printing.

made into a solidmade into a solid

I then create face groups of the parts I want as separate .stls and generate a complex (auto-generate).

face groupsface groupscomplex generatedcomplex generated

complex generated from other sidecomplex generated from other side

this is when the first problem occurs. The green lines seem to indicate an error (?) because in the next step, when I try to split the complex they turn into red lines and will not split from the rest of the stl.

red lines after complex splitred lines after complex split

I've tried quite a few different solidification variants and sometimes it works, sometimes it doesn't. I don't have the problem at the same face group every time. Does anyone know a better way to do it?


Message 2 of 10
in reply to: zieschang

The issue your facing is that GenerateComplex is that this tool works only for a single boundary towards the same group. In your case the sphere groups are connected to a single tube group at least two times. If such a case happens GenerateComplex creates a single complex surface only. This is indicated by the green lines. They are no errors but the  cases where the tool did its job. All other "intersections" are not filled and leave an open boundary (blue).

Here are working and not working cases:


From left to right:

1: The bright blue group touches the orange group twice > no fill at the second touch

2: The green group touches the four times > only the first touch is filled

3: The pink and the orange group touch the dark orange group twice  > only one per combination is filled

4: The green group touches the pink group and the orange group one time, same for the yellow group > all touches are filled

5: As there are five groups each group can touch another one one time only > all touches are filled.


To achieve a working group structure on your object I'd run MakeSolid in SolidType: SharpEdgePreserve (guess there are primitive objects spheres and cylinders as its source object). Don't forget to hit Update (lasts longer but should give sharp edges at the intersections). Now do EDIT/GenerateFaceGroups. In EdgeAngle mode you might need to pull the AngleThreshold to get a single group for each sphere and cylinder. Also if there maybe same colors for the groups on different regions now (there a limited amount of colors): Each region is an individual group now (as in case 5).


AutoGenerating a Complex now should give a green line on each group boundary now. Splitt the complex and Combine all elements you want to print in the same color. 

Gunter Weber
Triangle Artisan

Message 3 of 10
in reply to: MagWeb

Hi MagWeb,


thank you for your detailed response!

I tried creating face groups for every cylinder and sphere:


this seems to return mostly green lines when I generate the complex:




but when I then split the complex it returns red lines




Message 4 of 10
in reply to: zieschang

Do some of the tubes intersect outside of the spheres? If yes, this can't be handled by GenerateComplex as well. 

Ohne Titel.jpeg

Think that's the reason why you don't get all splitting properly...


Instead of using the Complex tool you also may try a Boolean attempt:

Separate all spheres as a single object before doing a MakeSolid and duplicate this spheres object. Hide one of these.

Now run MakeSolid on the remaining tubes structure.

Activate the MakeSolid result and activate the visible spheres object too (Hold down Shift while clicking to activate more than one object). The order of activation is important as you want to do a subtraction now (A-B different to B-A)

Run EDIT/BooleanDifference and show the hidden spheres.


Gunter Weber
Triangle Artisan

Message 5 of 10
in reply to: MagWeb

thank you so much! The boolean method works perfectly!

Message 6 of 10
in reply to: MagWeb

I do not understand. could you put some pictures t oshow me where going to?

Message 7 of 10
in reply to: Anonymous

S = A (white)+B (red):

Scene.jpegA = :


B =:


BouleanDifference (A-B) gives X:

Ohne Titel 6.jpeg

Print X(as some color) plus B (as some different color)....

Gunter Weber
Triangle Artisan

Message 8 of 10
in reply to: MagWeb

sorry for my English lol
thanks you very much for your answer.
But could you explain me how you manage to do that boolean action? step by step please.
When I have the STL open in Meshmixer, try to explain me where I have to go to separate each part, save one by one and manage to print full of part.

Message 9 of 10
in reply to: Anonymous

If you loaded a STL with several not connected shells (e.g. the spheres and the connecting structure as above).

The first step is to get a separate object for each element: Run EDIT/SeparateShells.

> The upper example should result in 4 objects (three sphere objects and the structure)

Second step is to get a combined object for each color. While holding down SHIFT click on all objects which shall be printed in the same color (Hold down SHIFT and click on the three spheres). If there's more than a single object activated in the scene the EDIT options change. Now there's Combine. Do it to join.

> The upper example should result in 2 objects (a object out of three spheres and the structure)

Third step is to subtract the spheres from the structure. As this step will loose the spheres we need to do a copy before: Activate the spheres object and do EDIT/Duplicate. Hide this  duplicate via the eye icon in the scene browser.

Now activate the structure object  as the first object and holding down Shift the combined spheres object after that. If there are exactly two objects active in the scene the EDIT options show the Boolean operations. Run BooleanDifference to subtract the spheres from the structure.

When this operation is done, show the hidden duplicate again.

Gunter Weber
Triangle Artisan

Message 10 of 10
in reply to: MagWeb

I just posted an issue about remeshing and complex. Seems to be same type of issue. Make solid seems to be solving a lot of the issues. Thanks MagWeb and others


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